Restaurant and food-related industries demand plastic containers for food storage and transportation that are economical to purchase, effective in preserving food, effective in containing the food and its related moisture, attractive to the consumer, and easy to operate. One of the most important features for hinged plastic containers is the hinge design, which is critical to many of the above-described performance characteristics.
Prior art hinge designs include a “box hinge” shown in FIG. 1(A), a “W” hinge shown in FIG. 1(B), a two-point hinge shown in FIG. 1(C), a three-point hinge shown in FIG. 1(D), and a cylindrical hinge shown in FIG. 1(E). These prior art hinges are unacceptable for many reasons. For example, the box hinge is difficult to thermoform with its many sharp angles. And, due to the draw ratio of the box hinge, the resulting box hinge is often malformed. It is also often difficult to form a box hinge using polypropylene, a plastic material preferred in many plastic container applications.
The “W” hinge is difficult to consistently form owing to its many sharp angles. The depth of the “W” hinge is larger than the width of either of its side portions. The “W” hinge may also retain too much “memory” and may tend to close by itself. The memory of plastic containers refers to the inherent tendency of the plastic container to return to its determined position. For example, a container with too much memory may tend to automatically close when opened, much to the disgust of the end user, who could be attempting to remove the contents of the container or eat from the container. It is preferred that a container, once opened, will remain opened, and that a container, once closed, will remain closed.
The two-point and three-point designs are also more difficult to consistently form during manufacturing as they have multiple compression points. A complicated manufacturing process results in a higher percentage of product not meeting quality specifications or consumer expectations.
The more complicated hinge designs, such as the two-point, three-point, and “W” are difficult to form consistently. Many plastic containers are made by a thermoforming process, which only allows a few seconds to form the hinge. Thus, it is imperative that the hinge may be quickly and accurately formed.
The cylindrical hinge shown in FIG. 1(E) involves a coining process during manufacturing. The manufacturing of the cylindrical hinge involves a coining process. Coining processes generally involve the thinning of a plastic material at desired location(s). The coining of the cylindrical hinge may be accomplished using the compression force supplied by the forming press. If the cylindrical hinge is squeezed too much, a weakened, overly coined area may result in the hinge and cause product failure, i.e., the lid of the container tears away from the tray of the container at the hinge. Previous attempts to improve the manufacturing process of the cylindrical hinge have incorporated a revised cylindrical shape that leaves areas of a thicker plastic material along the coined region for reinforcement. The coined region of the cylindrical hinge is shown by reference numeral 2 and the reinforcing region is shown by reference numeral 4.
Other disadvantages of prior art hinges include poor closure of the container near the hinge. Poor closure of the container may result in leakage. The closure of the container near the hinge is especially susceptible to poor closure due to the physical proximity of the hinge to the locking profile of the container.
Another disadvantage of the prior art involves “narrow” windows for process operation. Many prior art containers require exacting specifications that may prove difficult for the manufacturer to economically meet and may result in considerable waste due to unacceptable product.